This invention relates generally to the field of cataract surgery and more particularly to a check valve for use in a handpiece for practicing the liquefaction technique of cataract removal.
The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of the lens onto the retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and lens.
When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL).
In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During this procedure, a thin phacoemulsification cutting tip is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquifies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by an artificial lens.
Recently, a new cataract removal technique has been developed that involves the injection of hot (approximately 45° C. to 105° C.) water or saline to liquefy or gellate the hard lens nucleus, thereby making it possible to aspirate the liquefied lens from the eye. Aspiration is conducted with the injection of the heated solution and the injection of a relatively cool solution, thereby quickly cooling and removing the heated solution. This technique is more fully described in U.S. Pat. No. 5,616,120 (Andrew, et al.), the entire contents of which is incorporated herein by reference. A commercially available handpiece used to practice this cataract removal technique is described in U.S. Pat. No. 6,860,868 (Sussman, et al.) and sold as the AQUALASE® handpiece by Alcon Laboratories, Inc., Fort Worth, Tex. The handpiece disclosed in this reference (e.g., handpiece 201 as seen in FIG. 2) uses a check valve to prevent the pressurized pulses of heated fluid from being forced backwards through the handpiece toward the irrigation fluid source. The check valve has a stopper or ball that is pressed against a valve seat by a spring, so that the valve is normally closed at ambient conditions. The inventors have found that during autoclaving, mineral residue from the irrigation fluid can build up around the stopper and seat, affecting the performance of the check valve. In addition, check valves that are closed completely require some initial force to open, thereby reducing the efficiencies of the handpiece at lower operating pressures, and making the check valve very sensitive to the spring rate and load force variability.
Therefore, a need continues to exist for a check valve with increased performance and reduces sensitivity to spring rate, load force variability and mineral deposits.